I began performing breathwork when I started doing the Wim Hof Method.  I continue to perform my breathwork much the same as Wim and his students do, but no longer finish with pushups.  I do, however, hold my breath when doing Stronglifts.  I started out only being able to hold my breath for about a minute, but have worked up to being able to hold it for as long as 3 minutes and 30 seconds.

Below is a spreadsheet containing all the data associated with my breathwork.  It contains the following categories:

Date, Time Session 1, Times Session 2, Time Session 3, Time Session 4, Pushups